Rich at idle? Shouldn't the idle mixture screws take care of that as long as the carb is working properly and the fuel pressure isn't blowing fuel past the needle and seat? I can see a little extra initial timing might help with that.
This carb was rich everywhere. At idle. Under acceleration. You name it, it was trying to drown itself. I only mention at idle because that's when my eyes were watering the most. Lol
These neighbors are from Monmouth CA which is at 7,000ft. We're now at 2800ft. I don't think they ever adjusted the carb while living at altitude, so this motor was trying to drink itself to death from the day it was installed. Their initial timing was around 9°-10° if I remember correctly. It was a dog. Once we leaned it out, that old girl was chooching!